536 



SCIENCE 



[N. S. Vol. LIV. No. 1405. 



orated, will mark an epocli in the study of 

 heredity, being apparently the first successful 

 attempt to deal experimentally with a partic- 

 ular factor or set of factors in the germ- 

 plasm. 



There remains another question we must 

 try to answer before we close, namely, " What 

 share has the mind taken in evolution ? " 

 From the point of view of the biologist, de- 

 scribing and generalizing on what he can ob- 

 serve, evolution may be represented as a series 

 of metabolic changes in living matter molded 

 by the environment. It will naturally be ob- 

 jected that such a description of life and its 

 manifestations as a physico-chemical mechan- 

 ism takes no account of mind. Surely, it will 

 be said, mind must have affected the course of 

 evolution, and may indeed be considered as the 

 most important factor in the process. Now, 

 without in the least wishing to deny the 

 importance of the mind, I would maintain 

 that there is no justification for the belief 

 that it has acted or could act as something 

 guiding or interfering with the course of 

 metabolism. This is not the place to enter in- 

 to a philosophical discussion on the ultimate 

 nature of our experience and its contents, nor 

 would I be competent to do so; nevertheless, 

 a scientific explanation of evolution can not 

 ignore the problem of mind if it is to satisfy 

 the average man. 



Let me put the matter as briefly as possible 

 at the risk of seeming somewhat dogmatic. 

 It will be admitted that all the manifestations 

 of living organisms depend, as mentioned 

 above, on series of physico-chemical changes 

 continuing without break, each step deter- 

 mining that which follows; also that the so- 

 called general laws of physics and of chem- 

 istry hold good in living processes. Since, 

 so far as living processes are known and un- 

 . derstood, they can be fully explained in ac- 

 cordance with these laws, there is no need and 

 no justification for calling in the help of any 

 special vital force or other directive influence 

 to account for them. Such crude vitalistic 

 theories are now discredited, but tend to re- 

 turn in a more subtle form as the doctrine 



of the interaction of body and mind, of the 

 influence of the mind on the activities of the 

 body. But, try as we may, we can not con- 

 ceive how a physical process can be inter- 

 rupted or supplemented by non-physical agen- 

 cies. Rather do we believe that to the con- 

 tinuous physico-chemical series of events there 

 corresponds a continuous series of mental 

 events inevitably connected with it; that the 

 two series are but partial views or abstrac- 

 tions, two aspects of some more complete 

 whole, the one seen from without, the other 

 from within, the one observed, the other felt. 

 One is capable of being described in scientific 

 language as a consistent series of events in 

 an outside world, the other is ascertained by 

 introspection, and is describable as a series 

 of mental events in psychical terms. There 

 is no possibility of the one affecting or con- 

 trolling the other, since they are not inde- 

 pendent of each other. Indissolubly con- 

 nected, any change in the one is necessarily 

 accompanied by a corresponding change in the 

 other. The mind is not a product of metab- 

 olism as materialism would imply, still less 

 an epiphenomenon or meaningless by-product 

 as some have held. I am well aware that the 

 view just put forward is rejected by many 

 philosophers, nevertheless it seems to me to 

 be the best and indeed the only working hy- 

 pothesis the biologist can use in the present 

 state of knowledge. The student of biology, 

 however, is not concerned with the building 

 up of systems of philosophy, though he should 

 realize that the mental series of events lies 

 outside the sphere of natural science. 



The question, then, which is the more im- 

 portant in evolution, the mental or the physical 

 series, has no meaning, since one can not hap- 

 pen without the other. The two have evolved 

 together pari passu. We know of no mind 

 apart from body, and have no right to assume 

 that metabolic processes can occur without 

 corresponding mental processes, however sim- 

 ple they may be. 



Simple response to stimulus is the basis of 

 all behavior. Responses may be linked to- 

 gether in chains, each acting as a stimulus to 



